1. Field of the Invention
Heterogeneous catalytic gas phase methane production from hydrogen and carbon dioxide is achieved directly at temperatures as low as 25.degree. C. and at atmospheric pressures by use of a catalyst having a mixture of Ru and RuOx, wherein x is greater than 0 and equal to or less than 2, supported by a suitable metal oxide support. Photo-methanation using such catalysts having photo excitable support materials significantly increases methane production, yielding almost stoichiometrically quantitative amounts of methane according to Sabatier reaction.
2. Description of the Prior Art
Use of ruthenium as a hydrogenation catalyst on a titania support for Fischer-Tropsch reactions of CO and H.sub.2 to produce hydrocarbons, principally liquid hydrocarbons at elevated pressure and methane at atmospheric pressure, is known from a number of patents including U.S. Pat. Nos. 4,042,614; 4,477,595; 4,558,030; 4,567,205; and 4,619,910. The 4,047,614 and 4,477,595 patents teach suppression of methane formation in the Fischer-Tropsch reaction when using titania as opposed to alumina or carbon support material.
Nickel is a known hydrogenation catalyst for reforming of methane by reaction of carbon monoxide and hydrogen. U.S. Pat. No. 4,132,672 teaches addition of a small amount of iridium for improved conversion of hydrogen and carbon monoxide to methane.
The electrochemical reduction of carbon dioxide to methane on Ru electrodes is taught by K. W. Frese, Jr. and S. Leach "Electrochemical Reduction of Carbon Dioxide to Methane, Methanol, and CO on Ru Electrodes", Journal of the Electrochemical Society, Vol. 132, No. 1, pgs. 259-260, January 1985. This electrochemical reduction works only at low current densities and is not a selective as desired for methane.
Photoreduction of CO.sub.2 to methane and higher hydrocarbons in aqueous solution using Ru or Os colloids as catalysts is taught by Itamar Willner, Ruben Maidan, Daphna Mandler, Heinz Durr, Gisela Dorr and Klaus Zengerle, "Photosensitized Reduction of CO.sub.2 to CH.sub.4 and H.sub.2 Evolution in the Presence of Ruthenium and Osmium Colloids: Strategies to Design Selectivity of Products Distribution", J. Am. Chem. Soc., Vol. 109, No. 20, pgs. 6080-6086, 1987. This photoreduction reaction utilizes Ru metal as an electron transfer catalyst and consumes triethanol amine making the process commercially unattractive.
The Sabatier reaction: EQU CO.sub.2 +4H.sub.2 .fwdarw.CH.sub.4 +2H.sub.2 O(g).DELTA.G.sub.298k .degree.=-27Kcal mol.sup.-1
is a known important catalytic process which despite its favorable thermodynamics, has been difficult to achieve due to high energy intermediates imposing large kinetic barriers and the formation of side products is common. Investigations during recent years aimed toward improving the activity and selectivity of methanation catalysts has been reported, including Lunde, P. J. and Kester, F. L., J. Catal. 30, 423-429 (1973); Phyng Quack, T. Q. and Rouleau, D., J. appl. Chem. Biotechnol. 26, 527-535 (1976); Tomsett, A. D., Hagiwara, T., Miyamoto, A. and Inui, T., Appl. Catal., 26, 391-394 (1986); Solymosi, F., Erdoheli, A. and Bansagi, T., J. Catal. 68, 371-382 (1981); Weatherbee, G. D. and Bartholomew, C. H., J. Catal, 87, 352-362 (1984); and Inui, T., Funabiki, F., Suehiro, M. and Sezume, T., JCS Faraday Trans. 1, 75, 787-802 (1979). Although progress has been made, elevated temperatures of greater than 300.degree. C. and pressures of greater than 1 atmosphere are still required for methane generation to proceed at significant rates and yields according to the Sabatier reaction.